Okay, I don't get it. Well, I sort of do - it's a nice way for readers to support indie bookstores. But at least in my town, most of the people who still go to indie bookstores don't eread. And people with ereaders don't go to bookstores. What would make them want to go to a bookstore now, vs. amazon (where they get an actual product description, instead of just a cover?)
At $0.36 a card (and that's if you order 1000), they're expensive to hand out as advertising (especially if you're selling a $0.99 book - not everyone will go collect the book, especially when they discover you have to know how to transfer a file to your ereader).
I can see doing a bigger display, with more information on the book, and then the cards. Maybe at indie bookstores, maybe at other local businesses and push the local author angle.
But most things sold on giftcards are commodities (minutes, credits, etc) or straight dollars, so you can do the actual choosing online or touching physical product.
It's a lot of hoops to jump through (go to the store, pick a book based on a card, go home and fiddle with your cables to get it onto your ereader vs. buy with 1-click on amazon). What's the upside for the reader?